The Smithsonian Air and Space Museum in Washington DC provide a "baby care" room where nursing mothers can use a s a quiet spot to breastfeed their infants or pump breastmilk when the moment requires.
Though not a dedicated nursing room, the room does offer a baby changing station also, but we are not certain whether their is an electric outlet to plug in a powered breast pump.
The museum also welcome nursing mothers to nurse throughout the museum at any comfortable spot the find. They recognize the legal right of moms to breastfeed in public according the US and Local state laws.
Note: Report mom-shaming or harassment while nursing in public or near lactation rooms (breastfeeding rooms), at Moms Pump Here mobile site https://www.momspumphere.com
Baby Care Room 600 Independence Ave SW, Washington D.C., District Of Columbia